In the past, electronic endoscope systems including a solid-state imaging device, for example, a charge-coupled device or a CMOS imaging device (generically referred to as a CCD) have been widely employed in the fields of medicine and industries alike. Among the electronic endoscope systems, the electronic endoscope system employed in the field of medicine is requested to have an insertion member thereof, which is inserted into a body cavity, made thinner. Moreover, the electronic endoscope system is requested to have the CCD made small-sized and designed to provide a larger number of pixels because of the necessity of producing a video signal that offers a high resolution.
Electronic endoscopes adopting the CCD fall into two types in terms of a method of producing a color video signal. One type of electronic endoscope uses a color filter to split light reflected from an object into three color light rays of red (R), green (G), and blue (B). CCDs produce image signals from the resultant red, green, and blue light rays at the same time. The other type of electronic endoscope adopts a so-called field-sequential technique that emits color illumination light rays of red, green, and blue to an object, and uses a single CCD to produce video signals from the color illumination light rays.
In order to make an insertion member included in an endoscope system thinner, the field-sequential technique is preferred. Besides, a video signal capable of providing a high resolution can be produced.
An electronic endoscope system adopting the field-sequential technique has been disclosed in Japanese Patent No. 2882609. The endoscope system disclosed in the Japanese Patent No. 2882609 will be described in conjunction with FIG. 5. An electronic endoscope system 51 comprises an endoscope 52, a light source device 53, a control device 54, and a TV monitor 55.
The endoscope 52 has an elongated insertion member 56 that is formed with a flexible member and inserted into a body cavity, and an operating member 57 proximal to the insertion member 56. A distal section 61 and a bending section 62 are successively joined to form the distal portion of the insertion member 56. The operating member 57 includes an operation knob 60 used to bend the bending section 62 of the insertion member 56. Moreover, the operating member 57 has a forceps port that communicates with a forceps insertion guide channel lying through the insertion member 56, and a knob used to supply water or air to a water/air supply nozzle, which is located in the distal section 61, over a water/air supply channel. Besides, one end of a universal cord 58 that connects the light source device 53 and the control device 54 is coupled to the operating member 57.
The light source device 53 includes a light source that emanates white light, such as, a xenon lamp, a lighting/driving mechanism that controls the lighting or driving of the light source, and a color filter that converts white light emitted from the light source into color light rays of red, green, and blue. Illumination light emanating from the light source device 53 is propagated over a light guide lying through the universal cord 58 and endoscope 52 alike, and irradiated to an object 63 from the distal section 61 of the insertion member 56.
The control device 54 has the ability to control the driving of a CCD incorporated in the distal section 61 of the insertion member 56. The control device 54 also has the ability to capture video signals, which the CCD produces from the red, green, and blue illumination light rays emitted from the light source device 53, and the ability to produce a predetermined television video signal from the red, green, and blue video signals.
On the TV monitor 55, a reproduced image based on the television video signal produced by the control device 54 is displayed.
The configuration of the light source device 53 will be described in conjunction with FIG. 6. White light emitted from the light source. 74 such as a xenon lamp is passed through a RGB rotary filter 73 that has color transmission filters 73R, 73G, and 73B for red, green, and blue arranged on the perimeter thereof. The white light falls on the proximal end surface of the light guide 19 via a condenser lens 75.
The RGB rotary filter 73 is driven to rotate at a predetermined rps by means of a motor 72. Light rays successively passed through the color transmission filters 73R, 73G, and 73B for red, green, and blue fall on the light guide 19.
The successive light rays of red, green, and blue falling on the light guide 19 are propagated over the universal cord 58, operating member 57, and insertion member 56, and then irradiated to the object 63 from the distal section 61.
A motor drive circuit 71 controls the rotational driving of the motor 72. The motor 72 has a frequency generator (FG) 72A. Pulses FG are produced with a rotation of the motor 72. This is attributable to electromotive force generated with a rotation of a magnet incorporated in the motor 72. For example, twenty-five pulses FG are produced with one rotation of the motor 72. The rotational frequency of the motor 72 will be discussed using the unit of fsc. The pulse frequency at which the frequency oscillator 72A produces pulses is 25 fsc. The pulse frequency of the frequency oscillator 72A is reported to a speed control circuit 77. Pulses produced at a pulse frequency of 4 fsc by a 4 fsc oscillator 78 are transferred at a one-sixth of the input frequency by a ⅙ frequency divider 44, that is, at a pulse frequency of ⅔ fsc. The pulse frequency of ⅔ fsc serves as a reference frequency that is compared with the pulse frequency of the frequency oscillator 72A. When the pulse frequency deviates from the reference frequency of ⅔ fsc, a rotating speed error voltage is produced.
On the other hand, the RGB rotary filter 73 has three silk-like reflectors 41r, 41g, and 41b arranged equidistantly concentrically. The reflectors give indices indicating open periods during which the color transmission filters 73R, 73G, and 73B for red, green, and blue are used. Sensors 42a and 42b are opposed to the reflectors 41r, 41g, and 41b. A pulse generated when the sensors 42a and 42b detects the reflector 41r, 41g, or 41b has the wave thereof reshaped by a pulse reshaping circuit 43. The resultant pulse is transferred to a phase comparing circuit 84.
The phase comparing circuit 84 receives pulses that have been produced at the pulse frequency of 4 fsc by the 4 fsc oscillator 78 and transferred at a quarter of the input frequency by a ¼ frequency divider 79. Furthermore, the phase comparing circuit 84 receives a vertical synchronizing (sync) signal (VD) from the control device 54.
To be more specific, a period during which the color transmission filters 73R, 73G, and 73B included in the rotary filter 73 transmit light corresponds to an exposure period during which the CCD is exposed. A period during which light is intercepted by the portion of the rotary filter 73 surrounding the color transmission filters 73R, 73G, and 73B corresponds to a period during which charge accumulated in the CCD is read into the control device 54 and a video signal is produced. In order to match the timing of the video signal with the timing of rotating the rotary filter 73, the phase of pulses produced when the sensors 42a and 42b detect the reflectors 41r, 41g, and 41b, the phase of the vertical sync signal VD contained in the video signal sent from the control device 54, and the phase of pulses transferred at the reference frequency fsc from the ¼ frequency divider 79 are compared with one another. Consequently, a phase error voltage is produced.
The speed error voltage produced by the speed control circuit 77 and the phase error voltage produced by the phase comparing circuit 84 are added up by an adder 85. Based on the resultant voltage, the motor drive circuit 71 controls the rotational driving of the motor 72.
Moreover, a type of endoscope other than the field-sequential type may be adopted as the endoscope 52. Japanese Unexamined Patent Application Publication No. 9-197294 has disclosed an endoscope in which the rotary filter 73 and motor 72 are removed from the path along which light emanating from the light source 74 is propagated to the light guide 19 via the condenser lens 75. In order to remove the rotary filter 73 and motor 72 from the light path, they are disposed as shown in FIG. 7. Namely, the rotary filter 73 and motor 72 are fixed to an L-shaped mounting bracket 91. Two rails 94, 94 are fixed to the bottom of a flange 92 that is a horizontally bent lower portion of the mounting bracket 91 while being parallel to each other. A sliding member 93 is attached to the bottom of the flange 92 so that it will enclose the rails 94 from the sides of the rails 94, 94. In other words, the sliding member 93 of the bracket 91 is attached so that it can freely slide in directions of arrows in FIG. 7 along the rails 94, 94.
A rack 95 is fixed to the side of the mounting bracket 91 on which the motor 72 is mounted. A worm gear 96 that is rotated by a motor 97 is meshed with the rack 95. By driving the motor 97 to rotate it forwards or reversely, the mounting bracket 91 slides in the directions of arrows in FIG. 7 by means of the worm gear 96 and rack 95.
Furthermore, switch pressers 99a and 99b are located at both ends of the flange 92 of the mounting bracket 91. Micro-switches 100a and 100b are opposed to the switch pressers 99a and 99b. The micro-switches 100a and 100b are located at a position at which the rotary filter 73 fixed to the mounting bracket 91 lies when moved to the path of light emanating from the light source 74 and a position at which the rotary filter 73 lies when removed from the path of light emanating from the light source 74.
Owing to the foregoing structure, depending on an object imaging technique implemented in the endoscope 52, the rotary filter 73 can be readily removed from the path of light emanating from the light source 74.
In the aforesaid conventional field-sequential type electronic endoscope system, the rotary filter 73 is disposed on the light path linking the light source 74 included in the light source device 53, the condenser lens 75, and the proximal end of the light guide 19 incorporated in the universal cord 58 coupled to the light source device 53. With the rotation of the motor 72, white light emitted from the light source 74 is passed through the red, green, and blue transmission filters 73R, 73G, and 73B included in the rotary filer 73. The resultant light is irradiated to the object 63 from the distal section 61 of the endoscope 52 over the light guide 19. The CCD incorporated in the distal section 61 of the insertion member 56 is exposed to reflected light rays of the red, green, and blue light rays which are reflected from the object illuminated with the red, green, and blue irradiation light rays. Consequently, red, green, and blue video signals are produced.
While the electronic endoscope system 51 is used to diagnose a body cavity, the rotational driving of the rotary filter 73 may be stopped for some reasons. When the rotary filter 73 is stopped rotating, for example, the red transmission filter 73R lies on the light path, an object picture signal produced by the CCD contains a red picture signal alone. When the rotary filter 73 is stopped rotating, for example, the non-transmission area of the rotary filter 73 between the red transmission filter 73R and green transmission filter 73G which does not transmit illumination light may lie on the light path. In this case, when the rotary filter is stopped during a period during which light is passed through the red transmission filter 73R and a red video signal is read, illumination light emanating from the light source 74 is intercepted by the non-transmission area of the rotary filter 73. The illumination light emanating from the light source 74 does not fall on the light guide 19. Consequently, no illumination light is irradiated to the object 63 from the distal section 61. Eventually, the CCD produces only a video signal representing a pitch-dark image. This cripples succeeding endoscopic diagnosis. Moreover, it is hard to pull the endoscope 52 out of a tortuous body cavity.
In this case, an operator drives the motor 97, which causes the mounting bracket 91, to which the rotary filter 73 and motor 72 are fixed, to slide, so as to rotate it. The operator then removes the rotary filter 73 from the path of light emanating from the light source 74. White light emanating from the light source 74 is irradiated to the object 63 from the distal section 61 of the insertion member 56 by way of the condenser lens 75 and light guide 19. The CCD produces a video signal while being exposed to the white light. With the help of an image displayed according to the video signal, the insertion member 56 of the endoscope 52 is pulled out of the body cavity.
However, the operator has to suspend endoscopic diagnosis because the illumination light is extinguished suddenly in the course of the endoscopic diagnosis or a picture is displayed in a specific color alone. The operator has to restart diagnosis using another electronic endoscope system 51. This poses a problem in that the operator and a person receiving the endoscopic diagnosis alike have to incur a heavy load.
The present invention attempts to break through the foregoing situation. An object of the present invention is to provide an illumination control system and an illumination control method for endoscope systems according to which in case the rotary filter is stopped for some reasons or the rotation of the rotary filter becomes abnormal anyhow, the rotary filter is immediately removed from the path of light emanating from the light source. Nevertheless, supply of illumination light that is white light is continued so that the endoscope can be continuously used. Thus, the load to be imposed on an operator and a person receiving endoscopic examination can be alleviated.